Definition:
Pycnodysostosis is an inherited disorder of the bone caused by a mutation in the gene that codes the enzyme cathespin K. This enzyme is important for normal bone cells called osteoclasts, to reabsorb into the bone and build new bone. The normal functioning of osteoclasts in individuals with pycnodysostosis is disrupted by a lack of cathepsin K, rendering individuals afflicted with this disorder to be unable to adequately reabsorb the component of bone called the organic matrix. This process, also called remodeling, is vital for normal bone maintenance. The bones in individuals afflicted with pycnodysostosis are abnormally dense and brittle as a result of this insufficient re-absorption process.

In 1996, the defective gene responsible for pycnodysostosis was located, offering accurate diagnosis, carrier testing and a more thorough understanding of this disorder.

Pycnodysostosis affects one in every 200,000 individuals in the United States.

Symptoms:
Pycnodysostosis results in short stature and abnormally dense and brittle bones. Height in affected males may reach four feet, while in affected females, measures are shorter. The bones’ brittleness in affected individuals commonly results in fractures, particularly in their feet, legs, and jaw. The fontanelle, the soft spot on the skull which normally closes when an infant is a few months old, remains open in affected individuals. Coarse facial features, abnormally short fingers, wrinkled skin, a small jaw, undeveloped and irregular teeth, dental cavities, and scoliosis are also common characteristics of this disorder.

Inheritance Pattern:
Pycnodysostosis is an autosomal recessive disorder.

Life Expectancy:
Life expectancy for Pycnodysostosis is normal.

Diagnosis and Testing:
A mutation has been found for Pycnodysostosis, rendering genetic analysis a necessary diagnostic tool to confirm this disorder. Prenatal genetic screening is available. X-rays may be used in combination with genetic testing to examine skeletal abnormalities.

Treatment:
Since bone fractures are a primary threat to those affected by Pycnodysostosis, it is important that care is taken to prevent or minimize tendencies for a fracture to occur. Such precautions include careful handling of an affected child, along with exercise and activities that are safe and do not require too much impact. Growth hormones have been shown to increase the bone growth and, thereby, the stature of individuals afflicted with Pycnodysostosis. Dental hygiene is especially helpful for affected individuals . The use of crutches or wheelchairs may be necessary and depend upon the progression of the disorder.